Ngorongoro Crater (Tanzania). At 610m deep and 260 sq km, this is the largest unflooded caldera in the world. A blue-green vision from above it's a haven for engangered wildlife and Maasai livestock. The crater was formed three million years ago when a giant volcano, which could have been as high as Kilimanjaro, exploded and collapsed. The caldera formed the concentric fractures in the crust cracked down to a magma reservoir deep underground. (Photo by John Bryant/Getty Images)

Viking re-enactors from the Gullinkambi group pose for pictures as part of the Jorvik Viking Festival on February 21, 2025. 100s of Viking re-enactors will march through the streets of York tomorrow. (Photo by James Glossop/The Times & Sunday Times)

Rajesh Babu, a police officer, wearing a helmet depicting coronavirus, requests a commuter to stay at home during a 21-day nationwide lockdown to limit the spreading of coronavirus disease (COVID-19), in Chennai, India, March 28, 2020. (Photo by P. Ravikumar/Reuters)

A rider picks up a hada, a traditional Tibetan ceremonial scarf, during a horse racing event of the 18th Mount Qomolangma culture and tourism festival in Xigaze, southwest China's Tibet Autonomous Region on June 20, 2023. (Photo by Sun Fei/Xinhua News Agency/Alamy Live News)

A cricket is seen posing on an advertising billboard during the Concacaf Nations League group stage football match between Costa Rica and Guadeloupe at the National Stadium in San Jose on September 5, 2024. (Photo by Ezequiel Becerra/AFP Photo)

Gabriella Papadakis and Guillaume Cizeron of France perform during the ice dance skating event at the ISU Grand Prix of Figure Skating final in Barcelona December 13, 2014. (Photo by Albert Gea/Reuters)

Midfielder Lindsey Horan (9) of Team United States and midfielder Kosovare Asllani (9) of Team Sweden go up for a header during the first round of the Tokyo 2020 Olympic Games at Tokyo Stadium on Wednesday, July 21. 2021. Sweden defeated the United States of America 3-0. (Photo by Toni L. Sandys/The Washington Post)

Visitors look at an artwork “Hierarchy of Prosperity” created by Indonesian artist Eko Nugroho during the VIP preview of the art fair “Art Basel” in Hong Kong, Tuesday, March 22, 2016. A set of gold-plated metal cubes, tapestries embroidered by unknown North Korean artisans and bales of cardboard waste are among the highlights of the Art Basel Hong Kong fair opening this week. (Photo by Kin Cheung/AP Photo)